J3/04-210

Date:     2004-01-14
To:       J3
From:     Walt Brainerd
Subject:  Clarification of function side effects

Date:
2003-12-03 at 20:00:34

Request number:
102

Name:
Walt Brainerd

E_mail:
walt@fortran.com

============================================
Number:

Title: Clarification of function side effects

Submitted by: J3

Status: For Consideration

References: Fortra 2003, Section 7.1.8.1

Basic Functionality: Clarify when a function (especially one with side effects)
must be executed. Perhaps a good example is the following.
Is the value printed for x predictable?

program side_effect ! This is a lot like NOTE 7.15.

   x = 2.0
   y = 0*f(x)
   print *, x, y

   contains

   function f(x)
   x = x + 1
   f = x
   end function f

end program side_effect

Rationale: The Fortran 77 interp on this subject was never used to
modify the standard in any way and members of J3 seem
to disagree on this issue, so that indicates to me that
it should be clarified.

Estimated Impact: It depends on the way we go.

If f doesn't have to be evaluated, and x is unpredictable,
the words in 7.1.8.1 need to be made stronger (clearer?).

If not, the sections needs a rewrite.

[Is my bias showing?]

Detailed Specification: Clarify the issue.

History: Submitted as Pub-102